Why Some People Can Get Away With Only A Little Sleep Every Night

Everyone has heard that it’s vital to get seven to nine hours of sleep a night, a recommendation repeated so often it has become gospel. Get anything less, and you are more likely to suffer from poor health in the short and long term — memory problems, metabolic issues, depression, dementia, heart disease, a weakened immune system Natural short sleepers, as they are called, are genetically wired to need only four to six hours of sleep a night. These outliers suggest that quality, not quantity, is what matters. If scientists could figure out what these people do differently it might, they hope, provide insight into sleep’s very nature. Most of what we know about sleep and sleep deprivation stems from a model proposed in the 1970s by a Hungarian-Swiss researcher named Alexander Borbély. His two-process model of sleep describes how separate systems — circadian rhythm and sleep homeostasis — interact to govern when and how long we sleep. The circadian clock dictates the 24-hour cycle of sleep and wakefulness, guided by external cues like light and darkness. Sleep homeostasis, on the other hand, is driven by internal pressure that builds while you’re awake and decreases while you’re asleep, ebbing and flowing like hunger. In a father-son pair of short sleepers, the researchers identified a mutation in another gene, NPSR1, which is involved in regulating the sleep/wake cycle. When they created mice with the same mutation, they found that the animals spent less time sleeping and, in behavioral tests, lacked the memory problems that typically follow a short night’s sleep. Based on the findings in short sleepers, some researchers think it may be time to update the old two-process model of sleep, which is how Ptáček developed the idea of a third influence. The updated model might unfold like this: In the morning, the circadian clock indicates it is time to start your day, and sleep homeostasis signals you’ve gotten enough sleep to get out of bed. Then a third factor — behavioral drive — compels you to go out and do your job, or find a mate, or gather sustenance. At night, the process goes in reverse, to calm the body down for sleep. The researchers are also interested in understanding other sleep outliers. Sleep duration, like most behaviors, follows a bell curve. Short sleepers sit on one end of the curve, long sleepers on the other. Fu has found one genetic mutation associated with long sleep, but long sleepers are challenging to study because their schedules don’t align with the norms and demands of society. Long sleepers are often forced to get up early to go to school or work, which can result in sleep deprivation and may contribute to depression and other illnesses.

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